1. Field of the Invention
The invention relates to gas springs, and in particular to gas springs having external locking means for retaining a piston rod in an extended position relative to a cylinder.
2. The Prior Art
Gas springs of this general type are useful, for example, in pivoting a trunk lid or hatch-back of an automobile between open and closed positions. When the trunk lid is raised and the gas spring is fully extended, it may be desirable, or necessary in the event of a gas leakage, to engage the mechanical lock to retain the lid in the fully open position.
An example of a gas spring with a locking device for locking the piston rod in its fully extended position is described in U.S. Pat. No. 4,078,779. The pneumatic spring according to this patent comprises a spring arm mounted on the outward end of a piston rod. The spring arm has apertures in it into which a pin provided on the cylinder locks when the piston rod is extended. To permit inward movement of the piston rod, the spring arm is pulled away from the cylinder, thereby disengaging the pin from the spring arm aperture in which it has been engaged.
U.S. Pat. No. 3,883,126 discloses a gas spring having a shield tube mounted on the piston rod, and a latch device comprising diametrically opposed spring arms provided on the apertured end of the cylinder. As the piston rod is extended, the shield tube rides telescopingly over the cylinder until the piston rod is fully extended and the shield tube is clear of the spring arms, at which point the spring arms move outwardly and form a surface against which the shield tube abuts, thereby preventing inward movement of the piston rod. To permit inward movement of the piston rod, the spring arms are manually compressed toward each other so that the shield tube again is able to ride telescopingly over the spring arms.
It is a disadvantage of these known gas springs that, even when unnecessary or undesirable, the external latching devices of these gas springs operate to restrain the piston rod in its extended position, unless and until they are disengaged, every time the gas spring is fully extended in its normal operation.
Thus, an object of the present invention is to provide a gas spring with an external locking mechanism that is not engaged during normal operation between its normal inward and outward positions, but only when specifically desired by its operator. For example, in the event of a gas leak rendering the gas spring inoperative, or rendering the gas spring unable to counterbalance the weight of a hood or trunk lid to maintain it in the open position, the consumer may use the present invention to retain the piston rod in an extended position.